This invention relates to a system for supporting ASN.1 (Abstract Syntax Notation One) protocol encoding/decoding in OSI (Open Systems Interconnection) presentation/application protocol. The invention is utilized for input and reference of a value which is the component of a PDU (Protocol Data Unit) which is described in accordance with ISO8824 and is encoded/decoded on the basis of the ASN.1 encoding rules in ISO8825.
Encoding of a PDU requires inputting a data value which is a component of the PDU, while decoding of a PDU requires referring to a data structure value which is a component of the PDU. Input or reference of such values can be performed by using a program that provides the interface conversion between an user program and a table (VTL: Value Tree List) with values corresponding to a data structure of a machine processable abstract syntax. In order to make such an interface program, a programmer must understand a complex data structure of an abstract syntax and then hand-code the complicated interface program. Therefore, some data are likely to be lost because of possible mistakes by the programmer when the data structure is complex, and moreover, many steps are required for understanding of the data structure itself.